1. Field of the Invention
The present invention relates to an apparatus for controlling a fuel cell vehicle having a fuel cell stack and an electric double layer capacitor which are connected parallel to each other as a power supply for a propulsive motor of the fuel cell vehicle, and more particularly to the art of limiting the electric energy that is outputted to the propulsive motor to propel the fuel cell vehicle.
2. Description of the Related Art
One known control apparatus for use on a fuel cell vehicle for controlling the supply of electric energy consumed by the fuel cell vehicle is shown in FIG. 4 of the accompanying drawings.
As shown in FIG. 4, the control apparatus has a fuel cell 102 as a power supply for a motor drive unit 101 which supplies electric energy to a propulsive motor 100 and electric accessories (not shown) such as an air-conditioning unit, etc. An electric double layer capacitor 103 is connected parallel to the fuel cell 102 for discharging electric energy to make up for a shortage of electric energy generated by the fuel cell 102 when the amount of reactive gases supplied to the fuel cell 102 becomes insufficient due to a response delay of a reactive gas supply unit 104.
A fuel cell control unit 105 detects an operating state of the fuel cell 102 based on the pressure (Pgas), the flow rate (Qgas), and the temperature (Tgas) of reactive gases (hydrogen and air) supplied to the fuel cell 102, and recognizes an upper limit amount of amount (Ifc_LMT) of the electric energy that can be outputted from the fuel cell 102 based on the detected operating state. An electric vehicle control unit 106 calculates a motor-requested electric energy (PD_REQ) which is required to energize the motor 100 based on the amount of depression (Ap) of an accelerator pedal on the vehicle and the rotational speed (Nm) of the motor 100.
A power supply management control unit 107 indicates a target amount of electric energy (Ifc_CMD) to be generated by the fuel cell 102 to the fuel cell control unit 105 depending on the motor-requested electric energy (PD_REQ) and an electric energy (Pload) consumed by the electric accessories. The power supply management control unit 107 also indicates an output limit electric energy (PLD) which represents an upper limit amount of the electric energy that can be outputted from the motor drive unit 101 to the motor 100, depending on the upper limit amount of generated electric energy (Ifc_LMT), to the electric vehicle control unit 106 so that the amount of electric energy generated by the fuel cell 102 will not become insufficient.
The fuel cell control unit 105 determines a command value of the supplied amount of reactive gases (CMP_CMD) for the reactive gas supply unit 104 in order to achieve the target amount of electric energy (Ifc_CMD). The electric vehicle control unit 106 determines a torque command (TQ_CMD) for the motor drive unit 101 so that the electric energy outputted to the motor 100 will not exceed the output limit electric energy (PLD).
As a result, the fuel cell 102 operates to generate an amount of electric energy depending on the motor-requested electric energy (PD_REQ). Since the electric energy outputted from the motor drive unit 101 to the motor 100 is limited to an amount equal to or smaller than the output limit electric energy (PLD), the amount of electric energy generated by the fuel cell 102 is preventing from becoming insufficient.
When water produced by an electrochemical reaction of the reactive gases is trapped in cell units of the fuel cell 102, the output electric energy of the fuel cell 102 is lowered. If the fuel cell 102 suffers such a malfunction, then its electric generating capability is reduced, and the upper limit amount of generated electric energy (Ifc_LMT) is also reduced. If the upper limit amount of generated electric energy (Ifc_LMT) is reduced, the output limit electric energy (PLD) is also reduced, lowering an upper limit of the torque command (TRQ_CMD) for the motor drive unit 101.
Therefore, when the fuel cell 102 malfunctions, causing a sudden drop of the upper limit amount of generated electric energy (Ifc_LMT), while the fuel cell vehicle is running, the output torque produced by the motor 100 is abruptly reduced due to a reduction in the upper limit of the torque command (TRQ_CMD). As a result, the driver and passengers of the fuel cell vehicle are likely to suffer anxiety and discomfort the instant the output torque produced by the motor 100 is abruptly reduced.
It is therefore an object of the present invention to provide a control apparatus for controlling a fuel cell vehicle to prevent the output torque of a propulsive motor from dropping sharply in the even of a malfunction of a fuel cell mounted on the fuel cell vehicle.
According to the present invention, there is provided an improvement over an apparatus for controlling a fuel cell vehicle having motor driving means for outputting electric energy depending on a given torque command to a propulsive motor, a fuel cell for use as a power supply for the motor driving means, and an electric double layer capacitor connected parallel to the fuel cell, for being charged by the fuel cell and discharged to supplement a shortage of an amount of electric energy generated by the fuel cell.
The apparatus comprises upper limit electric energy recognizing means for detecting an operating state of the fuel cell and recognizing an upper limit amount of electric energy generated by the fuel cell depending on the detected operating state, upper limit discharged electric energy recognizing means for recognizing an upper limit amount of discharged electric energy representing an amount of electric energy discharged from the electric double layer capacitor when the amount of electric energy generated by the fuel cell reaches the upper limit amount of generated electric energy, upper limit total electric energy recognizing means for recognizing an upper limit amount of total electric energy representing an upper limit amount of total electric energy which can be outputted from the fuel cell and the electric double layer capacitor, depending on the upper limit amount of discharged electric energy and the upper limit amount of generated electric energy, and torque command limiting means for limiting the torque command to at most an upper limit of torque depending on the upper limit amount of total electric energy.
The upper limit total electric energy recognizing means recognizes the upper limit amount of total electric energy depending on the upper limit amount of generated electric energy of the fuel cell and the upper limit amount of discharged electric energy of the electric double layer capacitor. Even if the fuel cell malfunctions and the upper limit amount of generated electric energy of the fuel cell which is recognized by the upper limit electric energy recognizing means sharply drops, a reduction in the upper limit amount of total electric energy is suppressed by an amount of electric energy discharged from the electric double layer capacitor.
The torque command limiting means limits the torque command to at most the upper limit of torque depending on the upper limit amount of total electric energy. When the fuel cell malfunctions while the fuel cell vehicle is running, the torque command for the motor is prevented from being abruptly reduced, thus preventing the output torque of the motor from being lowered. Accordingly, the driver and passengers of the fuel cell vehicle are prevented from suffering anxiety and discomfort due to a change in the behavior of the fuel cell vehicle which would otherwise be caused by a sharp decrease in the output torque of the motor.
The apparatus further comprises open voltage recognizing means for recognizing an open voltage across the electric double layer capacitor, and storage means for storing data of a characteristic map representing the correlation between the amount of electric energy generated by the fuel cell and the output voltage thereof and data of an internal resistance of the electric double layer capacitor, the upper limit discharged electric energy recognizing means comprising means for calculating the upper limit amount of discharged electric energy based on the output voltage of the fuel cell which is obtained by applying the upper limit amount of generated electric energy to the characteristic map, the open voltage across the electric double layer capacitor which is recognized by the open voltage recognizing means, and the internal resistance of the electric double layer capacitor.
The upper limit discharged electric energy recognizing means applies the upper limit amount of generated electric energy to the characteristic map, and can recognize the output voltage of the fuel cell from the characteristic map at the time the amount of electric energy generated by the fuel cell reaches the upper limit amount of generated electric energy. The upper limit discharged electric energy recognizing means can calculate the upper limit amount of discharged electric energy with accuracy, using the output voltage of the fuel cell at the upper limit amount of generated electric energy, the open voltage across the electric double layer capacitor, and the internal resistance of the electric double layer capacitor.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.